Well I'll add my .02.
I went the direction of the gloss epoxy finish and as mentioned it is a PITA to get right. I like to think I did a pretty good job and a few guys on here who have seen it in person can add their opinions. The oil finish is probably the easiest initial application but requires more maintenance down the line. Scratches and dings can damage the wood itself but they aren't as noticeable as some of the other applications. I have heard from multiple sources that thinning epoxy is not a good idea but it definitely makes it easier to apply. the downside is it does not build up a thick layer as quickly and scratches are not only noticeable but can damage the wood. The gloss finish is the hardest to achieve but if you put the time and effort in your prep can be done and is very thick. I have had a gloss finish on my gun and aside from a few very deep scratches it does not show most of the minor damage. If I wanted a matte finish I would use the same method as if I wanted a gloss finish and just sand it evenly by hand. This will eliminate the difficulties of a gloss finish by giving you the ability to sand out any imperfections but you will still have a nice thick protective layer.
Refinishing epoxy is not particularly difficult. Just a general sanding to allow for a mechanical bond and reapply. Its the same as with oil except achieving the perfect gloss finish can be difficult but if you're fine with matte than this isn't an issue.
I am currently working on a gun that I plan to epoxy and then sand/buff to a very high gloss. It will definitely be labor intensive but hopefully not as bad as the 12 or so coats I had to put on the first gun before I was happy. Part of the reason for this choice is the materials that I am using (maple and carbon fiber). If I built a gun out of all teak I would probably go with an oil finish.
